The present invention concerns a process for the preparation of dimethylethylamine: ##STR1## by the reaction of ethanol with dimethylamine according to the reaction: EQU C.sub.2 H.sub.5 OH+(CH.sub.3).sub.2 NH.fwdarw.C.sub.2 H.sub.5 --N(CH.sub.3).sub.2 +H.sub.2 O.
This reaction is carried out in the presence of hydrogen and of a hydrogenation/dehydrogenation catalyst.
Dimethylethylamine is an industrial product used as a polymerization catalyst for polyurethane resins principally used in the manufacture of foundry casting molds by the so-called `cold box` process.
The catalytic amination of alcohols in the presence of hydrogenation/dehydrogenation catalysts and, if need be, of hydrogen is already known in particular by Houben-Weyl, Vol. 11/1, pages 126 and following.
In a more precise manner, A. Baiker and W. Richarz (Industrial and Engineering Chemistry, Product Research and Development, 1977, 16 (3), pages 261 to 266) describe the catalytic amination of long chain aliphatic alcohols in the presence of various catalysts, among them copper and chromic oxide based catalysts.
However, during the dimethylamination of n-dodecanol, for instance, which is cited in Table III of page 265 of that article, these authors employ a molar ratio of (dimethylamine/dodecanol)=5.5, which during an industrial exploitation of this process results in a very large amount of recycling of the excess dimethylamine, bringing about a loss of productivity and a consumption of energy accrued in the form of vapor. The behavior of the catalyst with time, moreover, is not mentioned.
French patent No. 2,320,287 describes the reaction in the liquid phase, of long chain alcohols with primary or secondary N-methylated amines in the presence of copper chromite. However, the reaction times are long (5 to 7 hours in the examples of discontinuous operations), and the alkylamination is carried out in a complex equipment set-up, resulting in a low productivity and expensive upkeep. The use of catalysts in very finely powdered form implies extremely long filtration times, above all in the presence of viscous products like long chain N-methylated amines. Examples 1 to 8, giving a bracket for the concentration of dimethylamine in the circulation gas consisting of hydrogen for the essential part, do not permit a precise calculation of the molar ratio of (dimethylamine/alcohol) (thus the true consumption of dimethylamine), although it is possible to estimate that the latter is located in the vicinity of 1, that is to say in the vicinity of the theoretical molar ratio. Furthermore, no indication is given on the useful life of the catalysts being employed. Finally, the reaction temperature is such that this technique does not adapt itself to alcohols having a low boiling point, such as ethanol, on one hand because its use would require a high operating pressure in order to operate in the liquid phase and on the other hand because the first members of the series of aliphatic alcohols dehydrogenate at a much higher temperature than do the alcohols possessing longer chains.